Fred J. Davey

Orbitally induced oscillations in the East Antarctic ice sheet at the Oligocene/Miocene boundary

Between 34 and 15u2009million years (Myr) ago, when planetary temperatures were 3–4u2009°C warmer than at present and atmospheric CO2 concentrations were twice as high as today, the Antarctic ice sheets may have been unstable. Oxygen isotope records from deep-sea sediment cores suggest that during this time fluctuations in global temperatures and high-latitude continental ice volumes were influenced by orbital cycles. But it has hitherto not been possible to calibrate the inferred changes in ice volume with direct evidence for oscillations of the Antarctic ice sheets. Here we present sediment data from shallow marine cores in the western Ross Sea that exhibit well dated cyclic variations, and which link the extent of the East Antarctic ice sheet directly to orbital cycles during the Oligocene/Miocene transition (24.1–23.7u2009Myr ago). Three rapidly deposited glacimarine sequences are constrained to a period of less than 450u2009kyr by our age model, suggesting that orbital influences at the frequencies of obliquity (40u2009kyr) and eccentricity (125u2009kyr) controlled the oscillations of the ice margin at that time. An erosional hiatus covering 250u2009kyr provides direct evidence for a major episode of global cooling and ice-sheet expansion about 23.7u2009Myr ago, which had previously been inferred from oxygen isotope data (Mi1 event).

Drilling for Antarctic Cenozoic Climate and Tectonic History at Cape Roberts, southwestern Ross Sea

Since the early 1990s, the Cape Roberts Project has been working to document, through sediment drilling, the proximal record of Antarctic ice sheet history and climate for the southwestern part of the Ross Sea, Antarctica. It has also investigated the tectonic history of the Transantarctic Mountain range of the West Antarctic Rift system and its links to the separation of Australasia from Antarctica over the past 55 million years. The recovered sedimentary sequences and the information they contain provide a record of environmental conditions when global temperatures were similar to those proposed for the end of this century, a test for models of ice and climate behavior, and a better understanding of the tectonic evolution of the region.